Acrylonitrile synthesis



Aug. 26, 1952 Flled Oct 29, 1949 Allg 26, 1952 E. w. PlETRUszA ET AL 2,608,576

ACRYLONITRILE SYNTHESIS Filed oct. 29. 1949 2 ,SHEETS-#SHEET 2 FRESH CARR/ER GAS 'LOE-:- w --m 1 coNDENsE/z l 57; 9?

` co/voEfvsE/z i F/zAcr/oNAr/Na COLUMN PY/aoLYs/s REcYc/.Eo CHAMBER PHASE y CARR/ER' SEPARAToR f GAS 72 `93 l v s v 9 c 1 FRAcr/oNAr/Na 8]/ PHASE COLUMN 5 SEPARAro/z 9/ i 8f* 88 V* coNoE/vsE/z Vf "76 89 l WATER 93 ACRYL Y Il (L9-74 oN/TR/LE V 8G 96 EaP/JE@- V 1 MESH 97 RE-ao/LER 73 D/LUTEV HIGH B0/UNG H off/vH so H2504 SPRAY BY- PRooucrs AcRvLoNlT/a/LE 2 J2 coNoENsER A@ SEPA/anon H20*(NH+254 JNVENToRs.

EDWARD w. PlETRuszA` JOHN N. cosv ATTORNEY.

larlyhereinafter. Aembodiment of the present invention, high qualu rial's.

` drawings,

Patented Aug. 26, 1952 N UNITED STATES PATENT I OFFICE town, N. J assignors to Allied Chemical & Dye Corporation, NewYork, N. Y., a corporation of` `NewYork l Application October 29,

solutions to the above and other problems con- I fronting the art.` i

We `have now found that high quality acrylonitrile is produced by pyrolysis of the compound 3,3,3 nitrilotrispropanamide, the formula for which is N(CH2CH2CONH2)3. i l

Acrylates are suitable for preparation oi said tris-amide by reaction with ammonia, and are easily available, e. g. by synthesis from acetylene, `carbon monoxide, and an alcohol. `Alcohol em- -ployed to form an` acrylate may easily be recovered for reuseafter Vconversion of acrylateto tris-amide, as` will be pointed out more particu- Accordingly, `in a preferred ity acrylonitrile is obtained via 3,3,3 nitrlotris- .propanamide pyrolysisemploying only acetylene,

carbon monoxide, and ammonia starting'mate- Our; invention will now be more particularly described with reference to the accompanying which are iiow sheets illustrating diagrammatically one preferred mode of embodyingthe same. I

The drawings illustrate the 3 principal steps of a preferred embodiment of our process and the interrelation of said steps; Figure 1 illustrating mode of synthesizing acrylate by reaction of acetylene, carbon monoxide, and an alcohol; and mode of synthesizing, from acrylate and ammonia, 3,3,3-nitrilotrispropanamide and recov- /eringalcohol from reuse in step (l). vFigure 2 illustrates mode of pyrolyzing tris-amide from step (2) oriother source.

Commencing the description with the acrylate synthesis step: acetylene, and carbon monoxide inamountsl to make up, with recycled carbonyl, stoichiometric` proportions with the acetylene, are compressed by. compressor I and led via pipe 2 into a stainless steel synthesis tower 3, containing recycled alcohol. and anyfresh alcohol required for make up, recycled metal carbonyl formed from catalyst and carbon monoxide, and recycled catalyst and any fresh catalyst required for makeup.

`Methanol may be? taken-'as exemplary' of i alco- V1949, serial N9. 124,395 2 claims. (el. 260g-465.25"

hols used in our process. APreferably tower, 3 is filled to the top to utilize its full volume f or the reaction. The catalyst is preferably a halide of nickel, especially about l-2%, by weight of ,the alcohol, of nickel bromide or nickel iodide.

The `operating temperatures in synthesis tower 3 are ordinarily about l30l85 C. andthe operating pressures are ordinarily superatmospheric, e. g. about 5-50 atmospheres. Reaction rates are greater, the greater the operating pressure. Y Reaction is suitablycarried to about 1,0%- 80% concentration by weight of methyl acrylate.

Unreacted gases issuing from `the synthesis tower via line 4 separate from liquid products in gas separator 8 and are withdrawn for recycle via valve, 'I and line. Liquid productscontaining 40-80% acrylate and 60-20% alcohol by weight flow from gas separator 6 via valve 9 and line I I into Vsurge tank I2, and thence via valve I3 `and line I4 to fractionating column. I6. A polymerization inhibitor may be employed in the more concentrated acrylate solutions. u I A portion of the liquid product fromseparator B is recirculated .to synthesis tower 3 through `valved pipe IIJ; the quantity of product recircu- `separated into a reiiux stream controlled by valve I8 and a recycle stream controlled by valve I9 and passing through pipe 2I back to synthesis tower 3. Gases from condenser I1 pass via line 8 back to synthesis tower 3. The product side stream, controlled by valve 22, is passed into reboiler 23 via line 24. I i

Residue from reboiler 23 is returned via line 2B and valve 21 to column I6. Gases and vapors from the reboiler, coming off at about C.` to C., are passed to condenser 28, wherein vapors are condensed. The gases pass through line 29, together with recycled gases for recycle to acrylate synthesis tower 3. The condensate issuing from condenser 28 consists typically of at least about 46% acrylate and the balance chiefly alcohol. i

This crude acrylate-alcohol product requires n further purication. It is passed directly via line 3|, controlled by valve 32, to reaction chamber 33 for reaction with ammonia, preferably in presence of a hydroxylated solvent, especially those of elevated dielectric constant such as ethylene glycol, glycerol, water, etc. to form 3,3,3- nitrilotrispropanamide and alcohol corresponding to the acrylate used. Preferred processes for effecting the desired reaction of ammonia and an acrylate are disclosed and claimed in the copending application of one of us (Edward W. Pietrusza) Serial No. 119,990, led October 6. 1949. In these preferred processes the acrylate corresponds t0 a saturated monohydric alcohol having 1-4 carbon atoms in the molecule, especially methyl alcohol, and ammonia is present in excess. Ethylene glycol and glycerine are particularly eiective and are preferred as reaction media when a higher ester (e. g. ethyl, propyl, or butyl acrylate) is employed asreactant.

Acrylate-ammonia reaction chamber 33 is'provided with cooling coil 34 and agitator 36.y Operating temperatures are preferably about room temperature (Z5-30 C.) or below, e. g. downto minus C. Required make-up ammonia' and chambery 33 by pump'4lvia valve 42 and line 43 y' to serve as reaction medium in the next cycle, and another part is bled oi through valve 44 and line 46 for separation of reaction medium and by-products, and recovery of alcohol.

Suitably, the-alcohol recovery is effected in a first fractionati'n'gcolumn 41 wherein'an overheadfraction isv taken off at about 63-65 C'. Vapors are condensed in condenser- 48, -from which ammonia is withdrawn via line 49'for revuse in the tris-amide synthesis. v The condensed vapors, consisting chiefly of alcohol with some acrylate, are divided into a reflux stream controlled by valve 49 and a product stream passing via'valve 5I and pipe 52 to a second fractionating 'column 5'6. f' v Reaction medium and by-products collect as residue in the base of column 41 and are Withdrawn via line 53 controlled by valve 54, The by-products contain constituents pyrolyzable to acrylonitrile and accordingly the by-products are suitably submitted to pyrolysis together with or separately from the crude tris-amide.

In fractionating column 56V, Valcohol is collected as residue and recycled via line 5 1 and valve 58 for reuse in acrylate synthesis.` 'A' branch of line 5 1, controlled by valve 59, allows taking off recovered alcohol Afor delivery to alcohol wash tank 39. The distillate from column 56, coming off at about 65 C., is chiefly ammonia, alcohol, Vand any residual acrylate. It is condensed in cony denser 6l from which ammonia is withdrawn for recycle via pipe 49, reflux is returned viavalved line 62 to column 56, and alcohol-and acrylate are recycled via line 63 and valve chamber 33.

The crude tris-amide produce is dried in drier 64 tov reaction vburned 'offwith air.

4 66 heated by steam coil 61. Alcohol vapors drawn off are condensed in condenser 68 and returned via line 69 to tank 39. Tris-amide is withdrawn via a double valve arrangement 1|.

This crude tris-amide (or, if desired,w3,3,3 ni- 'trilotrispropanamide from. any; other source) is fed into pyrolysis chamber 12 (Fi'g.'2') Very satisfactory results are obtained when this chamber contains a solid contact material, silica gel or vmanganese oxide for example.

Operating temperatures are chosen to produce reaction in a reasonable-time. The best choice of tempera- 'tures'will dependv to some extent on choice oi contact material. A suitable range of temperature is, for example, between about 450 C. and about 550 C., as measured by a thermocouple in the hottest Azone of the pyrolysis chamber, When silica gel or manganese oxide is used as a contact material. n

In order to sweep the pyrolysis products (chiefly acrylonitrile, water and ammonia) throughthe pyrolysis chamber it isadvantageous to maintain a lowof carrier gases 'through the chamber. Thecarrier gases may be carbondioxide, nitrogen, steam or the like and may contain suiiicient oxygen or air to burn off deposits of tar or'carbon which might otherwise accumulatein 'the pyrolysis zone. Acrylonitrile is not highly se'nsi'tivexunder the conditions-of pyrolysis andltherefore the rate of introduction of tris-amide and carrier gases to the pyrolysis chamber is not highly critical in obtaining good yieldsro acrylonitrile.

It is desirable for'smoothoperation gto avoid possible undue accumulation of tris-amide in the relatively cool portions of the pyrolysis chamber near the point of introduction -of tris-amide. Such accumulations Vmay be avoided by providing mechanical agitation of hot solid-'contact material (such as powdered or pelleted'silica gel or other solid contact material)- in the inlet Zone of the pyrolysis chamber; rorby usingfluidized solid contact materialin tlrepyrolysis chamber.; fj

Regeneration ofthefcontact materilahvvhen required, is suitably-effected, if a stationarybedfis -used,`-by passing ,air -there'over to-burnoif deposits using temperatures of say 500i-60037 C.; Aor if the contact material is lluidiz'ed; the contact material is suitably regenerated byy separating it from reaction products and passing it through a regenerating-chamber wherein deposits are The products issuing -from the pyrolysis chamber are subjected to aneutraliration treatment to remove Vany free 4ammonia lcontained therein by'fa spray of dilute sulfuric'acid, d13.- When carbon dioxide or other acid-forming gasA or vapor is present in the pyrolysis mixture in amounts 'at least equivalent to the ammonia formed in the pyrolysis the ammo-nia forms a salt (e. gammeniumcarbonate) andl therefore need not be other- Wise neutralized. o Y Y Provision'is made for recyclingcarrier gas via blower 14 and line 16 an'dfoor bleeding oi gases via -vent 11e. g. ifairjis. added to the carrier gases to oxidize deposits' inthe pyrolysis chamber, gases must be released to prevent build up.v Lik'ewise, if airis usedto regenerate activity of a stationary ybed of contact-,material in the pyrolysis chamber, venting ofexhaust. gases is necessary. o -Driers and/or,foondensers18A `and 19 are interposedto removewater from gases'pa'ssed through the pyrolysis chamber since otherwise' fwater Would'build up as a result of its formationinthe tris-amidepyrolysis reaction. I

The product vapors are condensed and separated in condenser-separator 8| into an aqueous layer containing dissolved ammonium salt and an organic layer, mostly acrylonitrile. The organic layer passes via overflow line 82 controlled by valve 83 to fractionating column 84 wherein a product side stream is separated at about 76-78 C. and passed to reboiler 86.

An acrylonitrile-water azeotrope is taken ofi overhead at about 70-75 C. in fractionating column 84; it is condensed in an azeo-tropic head condenser 81 wherein it is separated into an organic phase which is returned to the column and an aqueous phase which is withdrawn via line 68 and valve 69. High boiling ley-products are withdrawn at the bottom of column 84.

The combined aqueous layers are passed to fractionating column 9|, wherein aqueous ammonium salt is withdrawn as residue and acrylonitrle-water azeotrope is taken oi at about 7075 C. as distillate and separated in azeotropic head condenser 92 into layers. The organic layer in part returns via line 93 to column 84 and in part reuxes into the top of column 9|. The aqueous layer reiiuxes into the lower section of column 9|, via line 93.

In reboiler 8'6, acrylonitrile entering via line 94 from column 84 is flash distilled and is then condensed in condenser 98 and withdrawn as iinal product in better than 90% yields on entering crude tris-amide. (The impurities associated with the tris-amide form a certain amount of acrylonitrile.) The residue in the reboiler is returned via line 91 to column 84.

Acrylonitrile produced by our process is found to be of high quality, substantially pure, and free of color forming and inhibitor impurities. Overall yields of acrylonitrile by our process abovedescribed, based on acetylene consumed, reach 85% of theory or better.

The foregoing description of apparatus and procedure is intended only to be illustrative of suitable means for carrying out our process, and is not intended in a limiting sense. It will be clear to one skilled in the art that the apparatus and procedures described may be extensively modified or may be replaced by other apparatus and procedures without departure from the scope of our invention. For example. in the tris-amide pyrolysis step, instead of solid tris-amide which is fed to the pyrolysis chamber, a solution of trisamide is suitable, e. g. tris-amide in the form of an aqueous solution of its formate salt. Nu-

merous other modifications" and changes of like scope may be made.

Appropriate pumps, conveyors, tanks, valves, control instruments, and other conventional items of equipment are employed at desired locations.

Operative temperatures are not conned to the range of 450-550 C. above set forth. Any temperatures may be used which are suiiiciently high to melt and vaporize the solid starting material and to bring about its pyrolysis under the conditions of catalyst, contact time, etc. in the reaction zone; however, the temperatures are desirably low enough to minimize side reactions such as decomposition of acrylonitrile to acetylene and hydrogenoyanide. The broad range of temperature employed is accordingly from about 350 C. to about 700 C., the lower temperatures being more suitable the more active the catalyst and the longer the contact time employed.

We claim:

l. A process for synthesis of acrylonitrile which comprises introducing 3,3,3-nitrilotrispropanamide into a pyrolysis zone, pyrolyzing said trisamide in vapor phase in presence of silica gel contact material at temperatures in the range between about 350 C. and about 700 C. with formation of acrylonitrile, and recovering acrylonitrile from the 3,3,3-nitrilotrispropanarnide pyrolysis products.

2. Process as deiinedin claim l, wherein temperatures in the hottest part of the pyrolysis zone are between about 450 C. and about 550 C.

EDWARD W. PIETRUSZA. JOHN N. COSBY.

REFERENCES CITED The following references are of record in the le or" this patent:

UNITED STATES PATENTS Number Name Date 2,120,933 Dittmar June 14, 1938 2,373,190 Kung Apr.. 10, 1945 2,375,005 Kung May 1, 1945 2,401,429 Kung June fi, 1946 OTHER REFERENCES Peck et al.: Interview with W. J Reppe, Fiat Final Report Number 273, pages 10-11 (Oct. 2, 1945). 

1. A PROCESS FOR SYNTHESIS OF CARYLONITRILE WHICH COMPRISES INTRODUCING 3,3,3-NITROLOTRISPROPANAMIDE INTO A PYROLYSIS ZONE, PYROLYZING SAID TRISAMIDE IN VAPOR PHASE IN PRESENCE OF SILICA GEL CONTACT MATERIAL AT TEMPERATURES IN THE RANGE BETWEEN 350* C. AND ABOUT 700* C. WITH FORMATION OF ACRYLONITRILE, AND RECOVERING ACRYLONITRILE FROM THE 3,3,3-NITROLOTRISPROPANAMIDE PYROLYSIS PRODUCTS. 